Methods of and apparatus for advancing and working thermoplastic materials

ABSTRACT

An extruder for thermoplastic material has a screw of a compression relief design for advancing and working the thermoplastic material to produce an extrudate at a more uniform temperature and with a more thorough mixing of thermoplastic materials than has been achieved in the past. A metering section of the screw is provided with pins for homogenizing the thermoplastic material with all of the pins in any one portion of the screw being arranged in a plane perpendicular to the axis of rotation of the extruder screw and directed radially outward from the axis of rotation. A helical flight formed on the extruder screw is uninterrupted in at least the metering portion of the screw.

United States Patent DeBoo et a1. Oct. 2, 1973 1 1 METHODS OF ANDAPPARATUS FOR 3,115,674 12/1963 Schrenk et a1 259/191 ADVANCING ANDWORKING 3,160,916 12/1964 Blakey, Jr t t t 259/193 2,581,031 1 1952Kuzik 259/191 THERMOPLASTIC MATERIALS 2,x(12,23x 8/1957 Colombo 259 192lnventors: Robert Victor DeBoo, Chicago, 111.;

Charles Bean Heard, Jr., Lawrenceville, Ga.

Assignee: Western Electric Company,

Incorporated, New York, NY.

Filed: Apr. 13, 1971 Appl. No.: 133,575

References Cited UNITED STATES PATENTS Munger et a1. 1. 259/191Pettersson 264/98 Tedder 259/191 Gwinn et a1. 425/207 X Barr et a1425/208 Primary Examiner-Harvey C. Ho rnsby Assistant Examiner-Alan l.Cantor Att0rneyW. M. Kain, J. B. Hoofnagle, Jr., R. P. Miller and A. C.Schwarz, Jr.

[57] ABSTRACT An extruder for thermoplastic material has a screw of acompression relief design for advancing and working the thermoplasticmaterial to produce an extrudate at a more uniform temperature and witha more thorough mixing of thermoplastic materials than has been achievedin the past. A metering section of the screw is provided with pins forhomogenizing the thermoplastic material with all of the pins in any oneportion of the screw being arranged in a plane perpendicular to the axisof rotation of the extruder screw and directed radially outward from theaxis of rotation. A helical flight formed on the extruder screw isuninterrupted in at least the metering portion of the screw.

41 Claims, 7 Drawing Figures n-COMPRESSION RELIEF SECTION 3 8 t 4, I I==LJ 7 /1' 28 20 42 22 1 3 Z FEED COMPRESSION SECTION SECTIONMETERlNG39SECTlON PATENTED 2 SHEET 10F 3 COMPRESSION RELIEF SECTION 38METERING QSECTION FEED s |oN COMPRESSION SECTION 1/ //\/l EN7'0/?$ Rl/06-500 c5: HEARD JR. BY (4) m FIG. 2

ATTORNEV PATENTEU 2'975 3.762.693

sum 20F a v PRIOR ART PRIOR ART FIG. 6

PATENTED 119T 3975 SHEET 30F 3 SLOTTED RING SCREW OUTPUT CURVE FOR SCREWEMBODYING PRINCIPLES OF THIS INVENTION I I I I IO 20 3O 4O 50 SCREWSPEED RPM.

EXTRUDER OUTPUT SCREW SPEED ON 8 20 l EXTRUDERS METHODS OF AND APPARATUSFOR ADVANCING AND WORKING THERMOPLASTIC MATERIALS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to methods ofand apparatus for advancing and working thermoplastic materials, andmore particularly to methods of and apparatus for advancingthermoplastic materials successively through feed, compression, relief,and metering zones with facilities being provided in the metering zonewithout interrupting the helical flight of the extruder screw forobtaining a high degree of thermal uniformity by an improved mixing ofthe thermoplastic materials.

2. Description of the Prior Art In the extrusion art, and especially inthe extrusion of thermoplastic materials for insulating conductors forcommunications needs, there is an increasing demand for equipment ofhigher output rates. The output rates for extrudates coveringconductors, which have somewhat thin cross section, are governedsomewhat by the maximum rate at which extrusion can be performed withoutintroducing defects in the products due to a lack of uniformtemperature. For example, an extruder for spinning yarn ends is operatedbeyond a practical rate thereof when the filaments passing therefrom aresusceptible to breakage during processing or exhibit an unacceptablevariation in denier. When the extrudate is a sheet, film variations inthe thickness of the film are indicative of an improper rate ofextrusion. Generally, the lack of temperature uniformity which manifestsitself by defects such as nonuniform dimensions or re duced strengthcharacteristics evinces a failure to achieve a thorough mixing of thethermoplastic material or materials within the extruder.

For experimental purposes, a mixture of pellets of a clear thermoplasticmaterial of a polyethylene or polyvinylchloride base together with avery small percent, e.g., l per cent, of color concentrate pellets maybe fed into a barrel of an extruder. The small amount of colorconcentrate mixes with the clear compound material when melting occursso that the melt regions become colored and are easily distinguishablefrom the un melted material. Once melting has begun, three distinctregions are noted in a cross section ofa channel formed by a helicalflight on an extruder screw. These are (l) the unmelted plastic or solidbed, (2) a thin melt film between the solid bed and the barrel, and (3)a melt pool where melted material collects. The percentage of unmeltedplastic can be evaluated as a function of position in the extruder.

The thermoplastic material begins to melt along the interface with theinner surface of the barrel. Then, as the flight of the extruder screwadvances, the flight wipes off the melt and forms a melt pool on theupstream side of each section of the channel formed by the turns of theflight. Some of the solid materials become tacky but may resist mixingand being transferred into a molten state thereby detracting from thehomogeneity of the mix.

It has been found that better mixing and temperature distribution arepossible through the use of relatively expensive extruders of increasedbarrel length to diameter ratios. A discussion of several availableextruder screw designs is given in a paper, An Operating Evaluation ofVarious 8 Extruder Screws Using an Infra-Red Thermometer, by R. V. DeBooand W. B. Beck, pre pared for the 16th Annular Symposium on Wire andCable, Nov. 29, and 30 and Dec. 1, 1967.

In one screw design, commonly referred to as an immediate compressiondesign, the root diameter of the screw increases uniformly forapproximately fourteen turns along the axis of the screw followed by ametering section of approximately six turns. The depth of thecompression section at the small diameterend thereof is approximately859 mils whereas the depth along the metering section which has auniform diameter is approximately 172 mils.

In another prior art design screw, commonly referred to as aconventional metering screw, an initial section thereof has a constantroot diameter for approximately eight turns followed by a uniformlyincreasing root diameter section for six turns followed by a six-turnmetering section. In this conventional metering screw, the depth of thefeed section is approximately 688 mils and the depth of the meteringsection approximately 172 mils. The conventional metering screw has aslight advantage at higher revolutions per minute since the presence ofthe feed section insures an adequate supply of resin while at the sametime providing additional time for the resin to pick up barrel heat.This minimizes subjecting the resin prematurely to compressive shearforces. Considering the limiting depth of the metering zones, whichamount to approximately thirty per cent of the total screw length, theoutput for these screws has been regarded as acceptable.

Heat is usually applied from an external source to the extruder barrelin the compression section to raise the temperature of the material. Inthe metering section, the temperature of the material is: increased overthat of the barrel because of the energy that has been imparted to thematerial and hence, in that section, the barrel acts as a heat sink. Asthe successive portions of the material are advanced into the meteringsection, the materials have been generally thoroughly mixed. In themetering section, heat is distributed throughout the material so thatthe material is homogenized with respect to temperature, i.e., thermaluniformity.

A still further prior art screw design commonly referred to as acompression relief design is characterized in having a high output ofextrudate at a low temperature which is variable. The compression reliefdesign has a feed section of six turns with a depth of 750 mils, acompression section of six turns with a minimum depth of I50 mils, acompression relief section of onehalf turn with a maximum depth of 250mils and a metering section of 7% turns with a constant depth of 250mils. The compression relief design screw with its relatively deepmetering section is significantly better in performance in terms ofgreater output and has better temperature control than the two priorlydescribed screws.

The compression relief design screw is the genus screw design, whereasthe compression screw is a species thereof with a compression reliefsection of zero length. The compression screw design is somewhatdisadvantageous since it is difficult to manipulate independently thethree sections or the metering section without affecting the others.However, with the compression relief screw design, the metering sectioncan be adjusted and the compression relief section designed to join themetering section to the compression section.

A still further prior art screw design is commonly referred to as aslotted ring screw design which includes a feed section of four turnsfor a constant depth of 675 mils followed by a compression section offour turns with a minimum depth of 270 mils and a metering section of 12turns with a constant depth of 270 mils. The slotted ring screw designis characterized by a generally high output with good mixing and a hightemperature, the temperature being constant. Additionally, the slottedring screw design has a broken flight to permit mounting the slottedring to the root diameter portion of the screw. However, the slottedring screw design has the disadvantage of having a high shear heatingbecause of the longer metering section, the broken flight and thehydrodynamic action of the slotted ring.

The presence of the slotted rings in the just described design curtailsomewhat the output capability of the deep metering sections of thisscrew. Without the rings, a higher output may be achieved, but thetemperature of the material tends to be less and not as uniform as withthe rings present. Also, with the slotted ring design, and the brokenflight, there occur so-called dead spaces which tend to cause thethermoplastic material to back-up, especially when usingpolyvinylchloride as the extrudate.

It is an object of this invention to provide methods of and apparatusfor obtaining an output and a mixing at least as comparable with theslotted ring screw design without increasing the shear heating of thethermoplastic materials and hence a lower temperature.

The action of the screw, in addition to carrying the material throughthe bore, effects a physical blending of the thermoplastic particles anda shearing type of mixing between the materials at the cylinder borewalls and screw flight edges. A thorough mixing and blending of thematerial is necessary to provide a homogeneous melt and to obtain auniform extrudate. It is desirable to be able to use the material in aform having substantially the same properties of the material which ispurchased and tested. In order to achieve this goal, it is desirable toavoid any change in melt index.

It is therefore an object of this invention to provide methods of andapparatus for extruding materials which provide good temperatureuniformity with a minimum change in the melt index of the material.

In at least one prior art patent (see U.S. Pat. No. 3,486,193) a meltdispersing means is positioned in the root of the screw at least onescrew flight upstream of the discharge end of the metering section andextending outwardly into the annular space between the screw root andthe flight diameter to form alternating open and closed positions in theannular space. The dispersing means may be positioned one-half screwflight upstream of the discharge end of the first metering section andmay include a plurality of cylindrical pins positioned a circumferentialdistance about the screw root and extending in a plane perpendicular tothe screw axis out to the flight diameter of the screw, the screw flightbeing interrupted thereat. Alternatively, the dispersing means mayinclude a plurality of spaced apart square pegs extending radially fromthe root of the screw and positioned a full flight length befor thedischarge end of a first metering section and extending to within about0.0l inch of the flight diameter.

In still another prior art patent (US. Pat. No. 3,487,503), an extruderfor plastic material has a screw which is provided with pegs arrangedcrosswise of a channel between adjacent turns of one flight of the screwalong a section thereof sufficiently near the discharge end of theextruder so that the material received thereby will be in a plasticcondition. The row of pegs may be aligned parallel to the axis of thescrew or may follow the shortest direction between flight portionsdefining the adjacent turns of the flight. In this latter arrangement,the rows extend perpendicular to the direction of the channel ratherthan parallel with the extruder axis. The pegs of each row are instaggered relation with those of the adjacent row. Moreover, the pegsare of approximately the same height as the flight in all cases. Also,although some of the pegs in a portion of the screw lie in a plane thatmay be perpendicular'to the axis of rotation of the screw, there areother ones of the pegs in that portion which lie outside the plane andwhich have the axes thereof parallel to the plane.

' The arrangement of the pegs in such a fashion may restrict somewhatthe flow of the material.

It is thus an object of this invention to provide an extruder screwhaving a pin arrangement which provides a less restricted passage forthe materials than has been provided in the past.

Also in the prior art peg arrangements, say transverse across thechannel width, the number of pegs that may be used is somewhatrestricted since the distance'crosswise of the channel may be less thanthe circumference of the screw. If it would be possible to use anarrangement of pins about the circumference of the screw, more pinscould be mounted on the screw so as to achieve a finer division withless restriction resulting in finer homogenizing or a better mixing upof the material.

An object of this invention, and a feature which the prior art appearsto lack, is the provision of an extruder screw having facilities forbreaking up the solids in the material so that the solids are dissipatedin with the melt pool formed in front of the screw flight.

The term mixing" as commonly used in the extruding art may be regardedas an action which effects the random scattering of minute portions ofthe melt in the condition as discharged from the extruder. The melt maybe in a thermally uniform state because mixing has been carried out to adegree that any non-uniformity of heating is readily corrected bytransfer of heat from small hotter portions of the melt to the adjacentcooler portions.

The term dispersing" involves mixing on a more microscopic level inwhich particles of various compounds in the melt are uniformlydistributed. Dispersions may be prepared within the particles approachsizes on the order of a few molecules of thickness.

As used herein, the term flight diameter refers to a value equal totwice the distance from the center of the screw to a point in the edgesurface of a screw flight in a plane perpendicular to the axis of thescrew. The root diameter of the screw is the diameter of the shaft orshank or core about which the helical flight is formed. The flightdiameter is constant so as to maintain a contact clearance in thecylindrical core with the flight depth or root character being varied toprovide different degrees or blending in the extruder.

SUMMARY OF THE INVENTION It is an object of this invention to providemethods of and apparatus for advancing and working thermoplasticmaterials to homogenize the materials.

It is also an object of this invention to provide methods of andapparatus for advancing an extrudate and for working the extrudateoptimumly without overly restricting the flow of the material.

Another object of this invention is to provide meth ods of and apparatusfor improving existing conventional extruder screws to achieve greateroutput and extrudates of improved quality with structural modificationsinvolving minor costs.

Still another object is to improve the capacity of con ventionalextruder of conventional length-overdiameter (L/D) ratio to effectcomplete mixing of a material after reaching a plasticized state, andhigh thermal uniformity within the material just prior to beingdischarged or extruded.

A still further object of this invention is to provide methods of andapparatus for achieving greater output rates of extrudates by usingextruder screws having a deeper channel between the walls of the flightof the extruder screw, especially in the metering section thereof,without increasing the barrel diameter or length.

A method of advancing and working thermoplastic materials embodyingcertain features of the invention may include the steps of revolving atleast one channel about an axis of revolution to advance at least onethermoplastic material through the channel along a predetermined path,and subjecting the material to at least one plurality of forces exertedby force-producing components extending into the path, all of theforceproducing components in any one portion of the chan nel having atleast some portion of the axis of each of the components in the portionof the channel lying in a plane which is perpendicular to the axis ofrevolution, the walls of the channel being formed by surfaces, whichsurfaces intersect with the plane so that the walls of the channel areuninterrupted at the intersection with the plane.

An apparatus for advancing and working thermoplastic materials embodyingcertain features of the invention may include at least one channelgenerated about an axis of revolution, facilities for revolving the atleast one channel about the axis of revolution to advance at least onethermoplastic material through the channel along a predetermined path,and at least one plurality of force-producing components extending intothe path for subjecting the material to at least one plurality offorces, all of the force-producing components in any one portion of thechannel having at least some portion of the axis of each of thecomponents in the section lying in a plane which is perpendicularto theaxis of revolution, the walls of the channel being formed by surfaces,which surfaces intersect with the plane so that the walls of the channelare uninterrupted at the intersection with the plane.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and features of thepresent invention will be more readily understood from the followingdetailed description of specific embodiments thereof when read inconjunction with the accompanying drawings, in which:

FIG. 1 is an elevation view, partially in section, of an apparatus whichembodies certain principles of this invention and showing a conventionalcompression relief design extruder screw modified with a pinarrangement;

FIG. 2 is an enlarged fragmentary detail view of a portion of theextruder screw of FIG. 1 and showing one group of pins connected to acore of the screw;

FIG. 3 is an enlarged sectional view of the extruder screw andassociated barrel of FIG. 1 taken along lines 3-3 showing a plurality ofpins directed outwardly radially from a longitudinal axis of the screwand lying substantially in a plane perpendicular to the axis, the flightof the screw being uninterrupted in the section of the screw containingthe pins;

FIG. 4 is a detail view of a portion of a prior art extruder screw of aslotted ring design in which the screw flights are interrupted to permitmounting or forming of the slotted rings;

FIG. 5 is an enlarged sectional view of the slotted ring prior art screwdesign of FIG. 4 taken along lines 5-5 thereof;

FIG. 6 is a detail view of a portion of a prior art extruder screwhaving a pin arrangement with the pins arranged generally crosswise ofthe channel formed by the flight; and

FIG. 7 is a graph showing extruder screw output for compression relief,slotted ring screw designs and the screw design which embodies theprinciples of this invention.

DETAILED DESCRIPTION Referring now to FIG. 1, there is shown one type ofextruder arrangement which is used commercially in the extrusion art.There is shown an extrusion apparatus, designated generally by thenumeral 20, which includes a hopper 21 into which at least onethermoplastic material in the form of pellets is fed. The hopper 21communicates with an extrusion cylinder, designated generally by thenumeral 22, so that the thermoplastic materials are advanced from aninlet or receiving end 23 of the cylinder to an outlet or delivery end24 thereof where the extrudate is formed into a covering on a cable core(not shown), successive sections of which are advanced continuouslythrough an extruder head (not shown).

As can best be seen in FIG. 1, the extrusion cylinder 22 includes abarrel or casing 26 having an internal surface or revolution in the formof a cylinder bore 27 of uniform diameter formed therethrough andconnecting the receiving end 23 to the deliveryend 24. The extrusioncylinder 22 also includes a flange 28 at the delivery end 24 thereofwhich facilitates the attachment of adapters, dies and other auxiliaryequipment (none of which are shown).

In order to advance the thermoplastic material from the hopper 21 to thedelivery end 24 of the extruder 20, an extruder screw, designatedgenerally by the numeral 31, is disposed concentrically within the bore27. The extruder screw 31 includes a core 32, has an upstream end 33thereof adjacent the hopper 21, and a downstream end 34 adjacent thedelivery end 24. Moreover, the extruder screw 31 is ofa design commonlyreferred to as a compression relief design. As such, and beginning atthe upstream end 33 thereof, the extruder screw 31 includes,successively, a first constant root diameter section 36 of the core 32referred to as a feed section (see FIG. 1), a uniformly increasing rootdiameter section 37, referred to as a compression section, a uniformlydecreasing root diameter section 38, referred to as a compression reliefsection, and. a uniform diameter root section 39, commonly referred toas the metering section.

The extrusion screw 31 is manufactured to have a thread or flight 41formed helically about and extending longitudinally along the core 32.The flight 41 is formed to provide a groove or channel 42 formed by theroot diameter surface of the core 32 and facing side walls 4343 of theflight. The external diameter and pitches of the flight 41 are generallyidentical and constant along the length of the extruder screw 31 from apoint just beyond the entrance end 33 of the screw to the delivery end34 thereof. However, if desired, the pitch of the flight 41 may be madeto decrease slightly from the portion of the screw adjacent thereceiving end 23 of the bore 27 to the delivery end 24 thereof. Theleading face of the flight 41 is substantially perpendicular to the rootdiameter surface of the core 32 to provide for an improved deliveryaction.

The channel 42 formed between the opposing walls of the flight 41 andthe surface of the core 32 is generally rectangular in shape. It shouldbe clear that the area of the channel 42 is constant from the receivingend 33 to the beginning of the compression section 37.

Then the area of the channel 42 decreases to the com- 47-47 in the formof pegs or pins which are mounted individually in holes 4848 formed inthe core 32 of the extruder screw 31. The holes 48-48 are formed so thatthe centers thereof lie substantially in a plane which is perpendicularto a longitudinal axis of rotation of the core 32. Additionally, theholes 48-48 are formed in the core 32 so that when the pins 47-47 aremounted in the associated ones of the holes, the pins are directedradially outward from the longitudinal axis of the core 32.

It should be observed that the arrangement of pins 47--47 of thisinvention differs from that of prior art arrangements such as that shownin FIG. 6. For example, all of the pins 4747 in any portion of theextruder screw 31 have at least some portion of the axes thereof or ofthe pins themselves lying in the so-called plane of pins which isperpendicular to the axis of rotation of the screw.

The structural arrangement of the pins 47-47 with respect to the flight41 is established so that the cooperation therebetween minimizes thedead spaces" and maximizes the homogenizing actions. In order toaccomplish this, the flight 41 of the extruder screw 31 is uninterruptedat least in that portion of the screw whereat the pins 4747 are located.This overcomes some of the disadvantages of the interrupted pattern offlight typical of slotted ring design screws (see FIGS. 4 and The walls43-43 of the flight 41 of the screw 31 are formed by surfaces whichintersect with the plane containing the pins 4747 such that the surfacesare continuous through the plane. This feature of an uninterruptedflight 41 is shown clearly in FIGS. 2 and 3.

It has also been found that the positioning of the pin planes along thelongitudinal axis of the screw 31 is important in order to optimize thehomogenizing action of the pins. Most desirably the pins 47-47 arelocated along the metering section 39 of the extruder screw 31. The pins47-47 are placed in the metering section 39 since the pins are moreeffective there with the least restriction to the pumping action of thescrew. Additionally, four planes of pins 47-47 spaced evenly along themetering section 39 appear to yield the best results to date.

Of course, the number of pins 4747, their location, diameter and spacingmay vary according to a particular application of the extruder 20, themelt temperature, type of plastic shape extruded, type of materials fedto the extruder, diameter of the screw 31, and other pertinentvariables. The passage of the thermoplastic material through a plane ofthe pins 4747 brings about substantial mixing to achieve thermaluniformity throughout the mix. The number of groups of pins 47-47 may beincreased or decreased as necessitated by the degree of responsivenessof heating and mixing.

The holes 4848 may be drilled to a diameter requiring press fitting ofthe pins 4747. The pins 4747 may be positively anchored in the core 33by, prior to the insertions thereof, placing solder powder and flux inthe associated hole 48 and thereafter pressing the pin into the hole andapplying heat to the pin and adjacent core area until bonding has takenplace. As the pins 4747 are made ordinarily oversized with respect tolength, the outer end surfaces are ground, machined or otherwise trimmedto a contour conformity with the surface of revolution swept by theflight 41. Of course, the pins 4747 can be connected to the core 32 inany feasible manner which does not otherwise disrupt the cross-sectionalarea of the channel 42.

In one typical arrangement, the extrusion apparatus 20 includes a screw31 having a barrel diameter of 8 inches. The feed section 36 extends forsix turns of the flight 41 and has a depth of 750 mils. The compressionand compression relief sections 37 and 38, respectively, extend for 6%turns respectively and have minimum depths of I50 mils. Finally, themetering section extends for 7% turns and has a uniform depth of 250mils. If the compression section 37 is too short, the materials arecompressed in too short a time which results in excessive heat build-upthat could burn and degrade the thermoplastic material.

Four planes of pins 4747 are used with the upstream one of the planesbeing located one-half turn or one-half pitch downstream of thecompression relief section 38 of the screw 31. Alternatively, theupstream one of the planes is three-sixteenths inch downstream of thecompression relief section. The downstream one of the planes ispositioned at the downstream end of the screw 31 with the other twoplanes spaced uniformly between the other two planes.

As for the pins 47- -47, the pins may be cylindrical, three-sixteenthsinch diameter with the centers of the holes 48-48 thereof spaced atleast one-quarter inch apart on a circumferential circle about the core32. The pins 47-47 extend into the predetermined path of thethermoplastic materials along the channel 42 with the height of the pinsapproximately, but not necessarily, the height of the flight 41.

Of course, all of the pins 4747 in a portion of the metering section 39need only have a portion thereof in the plane associated with thatportion of the metering section. The pins 4747, instead of lyingsubstantially inthe plane with the pins directed radially outward, couldproject transversely out of the plane where it intersects the flight 41.Or the pins 4747 could be included in the plane but not necessarily bedirected radially outward from the axis of rotation of the core 32. Andfinally, it is within the scope of this invention that theforce-producing components 4747 need not be in the form of pins butcould be in the form of vanes such as is common in impeller wheels.

lt may also be important to the operation of the extruder apparatus 20in a particular application to have a specified ratio of thecircumferential area of the core 32 of the screw 31 between the pins tothe total area of the free ends of the pins 4747 in any one plane. Theextruder screw 31 which embodies the principles of this invention couldhave the pins 4747 arranged so that this ratio lies in the range of tol.

OPERATION Thermoplastic material, such as polyethylene, polymerizedvinyl chloride or the like in granular, powder or pellet form withsuitable fillers and/or pigments, is introduced into the hopper 21 ofthe extruder 20. Facilities, including a motor and gear reduction unit(not shown) are provided to turn rotatably the extrusion screw 31 toadvance the thermoplastic materialfrom left to right, as viewed inFIG. 1. The thermoplastic material is advanced through the channel 42between the walls of the flight 41.

As the thermoplastic material is advanced into the compression section37, compacting, softening, melting and mixing takes place therein as thecross section of the channel 42 decreases. The material in thecompression section 37 tends to be drawn out with a change in velocity.Then when the material enters'the compression relief section 38, thematerial tends to be retracted somewhat with accompanying change invelocity. The metering section 39 functions to tend to bring aboutuniformity throughout the material advanced therethrough with respect tothe temperature, composition and coloring. The barrel 26 may be heatedat selected portions thereof to increase the rate of plasticization ofthe material.

Thermoplastic materials generally have maximum temperatures at whichthey resist decomposition or other degradation. This is important so asto avoid over-heating within the extruder 20. Heat resulting from thework expended or the material processed by the extruder may besufficient to be the exclusive source of heat for effectingplasticization. Where the temperature between the melting point ormelting range of material and the decomposition temperature is small,facilities (not shown) for heating or cooling portions of the barrel andscrew core may be required.

The general direction of the melting material relative to the screw 30is lengthwise of the helical channel 42. Forpurposes of explanation, thechannel 42 may be regarded as having a helical axis extending lengthwiseof the channel midway between adjacent turns of the flight 41. Inaddition to this movement, the material flows transversely and in acurvilinear fashion about the axis. Each minute element of materialtraverses a path which is a helix having convolutions centered about theaxis which is also a helix. This movement is generated by the frictionalengagement of the inner barrel surface 27 with the outer surface of theplastic material. Because of heat transmission at the interface of thescrew flight 41 and the surface of revolution resulting from frictionalheating, or by heating or cooling equipment, a temperature gradientnormally exists which varies outwardly from the axis to the interface.

As the material is advanced through each of the circles or planes ofpins 47-47, the pins, depending upon the height thereof, penetratecorresponding heights of the material contained in the channel 42 todisrupt the normal cross section currents of the material and causemixing of the material. By using the pins 4747 in the manner described,a high degree of thermal uniformity of the extrudate is obtained. Thepins 4747 tend to overcome the tendency of the melt to migrate upstreamto the leading or pushing face of the flight 41. By using the pins 4747,the melt is urged-toward the trailing faces of the flight to mix themelt with the solids and achieve a homogeneous extrudate.

It should be observed that in the past, achievement of thermaluniformity of an acceptable degree was obtained principally through areduction of the depth of the channel 42 within the metering section 39.This of course had the unfortunate corollary effect of reducing thedelivery capability of the extruder 20. In FIG. 7 are shown outputcurves for extruder screws of typical compression relief and slottedring designs.

The present invention avoids a reduction in delivery capability thatwould otherwise be necessary to homogenize the material. Rather thanthin out the flow path of the melt stream to a low-capacity output, theex truder 20 which embodies the principles of the present inventiondivides the melt stream into a number of smaller streams thereuponexposingthe molten material to high shear rates for a short period oftime after which the small streams of material are merged again in amixed condition. As shown by the solid curve in FIG. 7, the screw 31which embodies the principles of this invention utilizes a deepermetering section 39 to obtain high output capability while at the sametime having good mixing to obtain thermal uniformity and overcome thetendency for the melt to drift upstream.

It should be realized that an additional benefit of this inventionaccrues in that presently used screws may be easily modified to includethe pins 4747. This permits the continued use ofpresent investment inplant and at the same time being able to increase the output of thepresent invention.

In one typical arrangement, in an 8-inch, 20/1 extruder for low-densitypolyethylene, the barrel temperature is maintained at 400F, and the melttemperature at 450F. The speed of the extruder screw 32, which includesthe pins 47-47, is 46 revolutions per minute to given an output of 1,400pounds per hour.

In another typical arrangement, in a 10-inch, 8 k l extruder, the lengthof the feed section 36 is 27.9

inches, of the compression section, 19.5 inches, of the relief section5.0 inches, and the metering section 30.0 inches. The depth of the feedchannel is 0.75 inches, of the'metering section 1.210 incheswith a screwlead of 6.5 inches. This design screw with the pin arrangement gives anoutput of 1,100 lbs. per hour at 43 revolutions per minute.

It is to be understood that the abovedescribed arrangements are simplyillustrative of the invention.

Other arrangements may be devised by those skilled in the art which willembody the principles of the invention and fall within the spirit andscope thereof.

What is claimed is:

1. A method of advancing and working thermoplastic materials, whichincludes the steps of:

revolving at least one channel about an axis of revolution to advance atleast one thermoplastic mate rial through the channel along apredetermined path; and

subjecting the material to at least one plurality of forces exerted byforce-producing components extending into the path and along axes whichintersect the channel:

all of the force-producing components in any one portion of the channelhaving at least some portion of the axis of each of the components inthe portion lying in a plane which is perpendicular to the axis ofrevolution;

any portion of the channel extending between the walls of the channeland a predetermined distance along the axis of revolution;

the walls of the channel being formed by continuous surfacesintersecting with the plane so that the walls of the channel areuninterrupted at the intersection with the plane.

2. The method of claim 1, wherein the channel is formed by a helicalflight generated about the axis of revolution.

3. The method of claim 1, wherein the axes of all the force-producingelements in any one portion of the channel lie substantially in theplane.

4. A method of advancing and working thermoplastic materials, whichincludes the steps of:

revolving at least one channel about an axis of revolution to advance atleast one thermoplastic material through the channel along apredetermined path;

the walls of the channel being formed by turns of a flight formed aboutand along the axis of revolution; and

subjecting the material to at least one plurality of forces exerted byforce-producing components extending into the path;

all of the force-producing components in the channel in any one turn ofthe flight having at least some portion of each of the components in theturn lying in a plane which is perpendicular to the axis of revolution;

the walls of the channel being formed by continuous surfaces,intersecting the plane so that the channel is uninterrupted at theintersection with the plane.

5. A method of advancing and working thermoplastic materials, whichincludes the steps of:

rotating an extruder screw having at least one helical flight formedthereon about an axis of rotation to advance at least one thermoplasticmaterial through a channel having walls formed by the flight; and

subjecting the material to at least one plurality of forces exerted byforce-producing components extending into the channel and along axeswhich intersect the channel; all the force-producing components in thechannel in any one turn of the flight having at least some portion ofthe axis of each of the components in the turn lying in a plane which isperpendicular to the axis rotation;

the at least one flight intersecting with the plane and being continuoustherethrough.

6. The method of claim 5, wherein at least some portion of each one ofall of the force-producing components in any one turn of the flight liesin the plane.

7. The method of claim 6, wherein all of the forceproducing componentsin any one turn of the flight lie substantially in the plane.

8. A method of advancing and working thermoplastic materials, whichcomprises the steps of:

advancing at least one thermoplastic material through a helical channelextending along and about an axis of revolution;

compressing the material;

relieving the pressure in the material; and

homogenizing the material by subjecting the material to at least oneplurality of forces subsequent to relieving the pressure in thematerial, the forces being exerted by force-producing components, allthe force-producing components in the channel in any one turn thereoflying substantially in a plane which is perpendicular to the axis ofrevolution and directed radially outward from the axis of revolution;

the helical channel having uninterrupted side boundaries at least alongthat portion of the predetermined path at which the force-producingcomponents are positioned.

9. A method of advancing and working thermoplastic materials, whichcomprises the steps of:

moving a core having at least one helical flight formed therealongrotatably about an axis of rotation to advance a thermoplastic materialalong a predetermined path;

compressing the material;

relieving the pressure in the material; and

subjecting the material to at least one plurality of forces subsequentto relieving the pressure in the material, the forces being exerted byforceproducing components;

all of the force-producing components along the core in any one turn ofthe flight having at least some portion thereof lying in a plane whichis perpendicular to the axis of rotation;

the flight intersecting with and being continuous through the plane.

10. The method of claim 9, wherein each one of the force-producingcomponents in any one turn of the flight lies substantially in theplane.

11. The method of claim 10, wherein forceproducing components aredirected radially outward from the axis of rotation.

12. A method of advancing and working thermoplastic materials, whichcomprises the steps of:

introducing at least one thermoplastic material into engagement with afirst zone of a screw mounted rotatably in a housing, the screw having ahelical flight formed thereon; moving the screw rotatably about an axisof rotation to feed the thermoplastic materials longitudinally along thescrew through a channel formed on the screw to a second zone of thescrew;

compressing the thermoplastic material in the second zone of the screwwhile the material isadvanced simultaneously through the second zone toa third zone;

relieving the pressure in the thermoplastic material in a third zone ofthe screw while the material is advanced through the third zone to afourth zone; and

advancing the thermoplastic material through a fourth metering zone ofthe screw while simultaneously homogenizing the material by subjectingthe material to at least one group of a plurality of forces exerted byforce-producing components spaced about the surface of the screw andextending into the channel,

all of the force-producing components creating the forces being in ametering zone of the screw and all of the force-producing componentsalong the me tering zone of the screw in any one turn of the flightlying in a plane perpendicular of the axis of rotation of the screw,being directed radially outward from the axis of rotation, and beingnonintersecting with the flight.

13. An apparatus for advancing and working thermoplastic materials,which comprises:

at least one channel having a base and side walls, the

channel being generated about an axis of revolution;

means for revolving the at least one channel about the axis ofrevolution to advance at least one thermoplastic material through thechannel along a predetermined path; and

at least one plurality of force-producing components extendinginto thepath and along axes which intersect the base of the channel forsubjecting the material to at least one plurality of forces;

all of the force-producing components in the channel in any one turnthereof having at least some portion of the axis of each of thecomponents in the section lying in a plane which is perpendicular to theaxis of revolution;

the walls of the channel being formed by surfaces in tersecting with theplane so that the channel walls are uninterrupted at the intersectionwith and are continuous through the plane.

14. An apparatus for advancing and working thermoplastic materials,which comprises:

at least one channel having a base and side walls, the

channel being generated about an axis of revolution;

means for revolving the at leastone channel about the axis of revolutionto advance at least one thermoplastic material through the channel alonga predetermined path; and

at least one plurality of force-producing components extending into thepath for subjecting the material to at least one plurality of forces;

all of the force-producing components in the channel in any one turnthereof having at least some portion of each of the components in theturn lying in a plane which is perpendicular to the axis of revolution;

the walls of the channel being formed by surfaces intersecting with theplane so that the channel walls are uninterrupted at the intersectionwith and are continuous through the plane.

15. The apparatus of claim 14, wherein the channel is formed by ahelical flight generated about the axis of revolution.

16. Apparatus for advancing and working thermoplastic materials, whichcomprises:

a channel generated helically about an axis for advancing at least onethermoplastic material along a predetermined path;

means for revolving the channel about the axis; and

at least one plurality of force-producing components extending into thepath along axes which intersect the channel and positioned along theaxis of revolution for subjecting the material to a plurality of forces,

all of the force-producing components in the channel in any one turnthereof having at least a portion of the axis thereoflying in a planewhich is perpendicular to the axis of revolution;

the walls of the channel being formed by surfaces, which surfacesintersect with the plane and which surfaces are continuous through theplane.

17. Apparatus for advancing and working thermoplastic materials, whichcomprises;

a housing having a longitudinally extending bore formed therein andhaving a longitudinal axis;

means disposed concentrically within the bore and having a flight formedhelically thereon and ex tending substantially from one end thereof tothe other for advancing a thermoplastic material from the one end to theother end thereof;

means for rotating the advancing means about the longitudinal axis; and

a plurality of means connected to the advancing means for homogenizingthe thermoplastic material, all of the homogenizing means in any oneturn of the flight being disposed substantially in one planeperpendicular to the longitudinal axis;

the helical flight being continuous in at least the portion of theadvancing means which contains the homogenizing means.

18. Apparatus for advancing and working thermoplastic materials, whichcomprises:

means including at least one channel for advancing at least onethermoplastic material along a predetermined path through the channelextending along the predetermined path; and

means for revolving the channel around an axis of revolution; and

a plurality of means in the advancing means and directed radiallyoutward from the axis of revolution for homogenizing the material; allthe means in any one turn of the channel lying substantially in a planewhich is perpendicular to the axis of revolution;

the walls of the channel being formed by surfaces, which surfacesintersect with the plane and are continuous therethrough so as to haveuninterrupted boundaries at least along that portion of thepredetermined path containing the homogenizing means.

19. Apparatus for advancing and working thermoplastic materials, whichcomprises:

a housing having a longitudinally extending cylindrical bore formedtherein,

an extrusion screw fitting closely within the bore and having a channelextending substantially from one end to the other end thereof generatedhelically about an axis of rotation of the screw, one end of the screwbeing a receiving end and the other end being a delivery end, foradvancing a thermoplastic material from the receiving end! of the screwto the delivery end thereof and for homogenizing the material;

the screw being formed successively from the receiving end to thedelivery end with a feed section, a compression section, a compressionrelief section, and a metering section, and

a plurality of means in the channel for subjecting the thermoplasticmaterials to a plurality of forces; all the means in any one turn of thechannel having at least an integral portion thereof disposed in oneplane which is perpendicular to the axis of rotation of the screw;

the walls of the channel being formed by surfaces intersecting with theplane so that the surfaces are uninterrupted and continuous through theplane.

20. The apparatus of claim 19, wherein the subjecting means is disposedwithin the metering section of the screw.

2]. The apparatus of claim 19, wherein the subjecting means includes atleast one group of a plurality of force-producing components with all ofthe forceproducing components in any one turn of the channel having atleast a portion of each of the force-producing components in that turnlying in the plane.

22. The apparatus of claim 21, wherein all the forceproducing componentsare positioned along the metering section of the screw, all of theforce-producing components in any one turn of the metering section ofthe screw lying substantially in the plane.

23. The apparatus of claim 22, wherein the upstream one of the at leastone group of components is spaced less than one turn downstream of thecompression relief section of the screw.

24. The apparatus of claim 23, wherein a second group of force-producingcomponents are positioned at the downstream end of the screw.

25. The apparatus of claim 24, wherein at least four groups of theforce-producing components are spaced along the metering section of thescrew, the middle two groups of components being equally spaced alongthe metering section between the upstream-most group and thedownstream-most group.

26. The apparatus of claim 19, wherein the subjecting means includes onegroup of a plurality of pins arranged about the circumference of thescrew, all of the pins in the at least one group lying substantially inthe plane all of the pins being within the metering section of thescrew.

27. The apparatus of claim 26, wherein the pins are directed radiallyperpendicularly of the axis of rotation of the screw.

28. The apparatus of claim 27, wherein the upstream one of the planes isspaced one-half the pitch of the screw downstream of the downstream endof the compression relief section of the screw.

29. A screw for advancing and working thermoplastic materials, whichcomprises:

a core having an axis of rotation for advancing a thermoplasticmaterial;

at least one flight connected to and extending outwardly from the coreto a surface of revolution concentric with the axis of rotation of thecore, the flight being generated helically about the axis of rotation;and

at least one plurality of force-producing components connected to thecore for subjecting the material to a plurality of forces, theforce-producing components extending beyond the core along axes whichintersect the core and spaced from the surface of revolution,

all of the force-producing components along the core in any one turn ofthe flight having at least some portion of the axis of each of thecomponents in the turn of the flight lying in a plane which plane isperpendicular to the axis of rotation;

the flight intersecting with and being continuous through the plane.

30. A screw for advancing and working thermoplastic materials, whichcomprises:

a core having an axis of rotation for advancing a thermoplasticmaterial;

at least one flight connected to and extending outwardly from the coreto a surface of revolution concentric with the axis of rotation of thecore, the flight being generated helically about the axis of rotation;and

at least one plurality of force-producing components connected to thecore for subjecting the material to a plurality of forces, theforce-producing components extending beyond the core and spaced from thesurface of revolution,

all of the force-producing components along the core in any one turn ofthe flight having at least some portion of each of the components in theturn of the flight lying in a plane which plane is perpendicular to theaxis of rotation;

the flight intersecting with and being continuous through the plane.

31. A screw for advancing and working thermoplastic materials, whichcomprises:

a core having an axis of rotation;

at least one helical flight extending outwardly from the core to asurface of revolution concentric with the axis of rotation of the core,the at least one flight defining a channel measured in a transversedirection between adjacent turns of the flight, and extending in ahelical path lengthwise of the core; and

a plurality of means for subjecting a thermoplastic material to aplurality of forces to homogenize the material; all the means in any oneturn of the flight disposed substantially in one plane which isperpendicular to the axis of rotation of the core;

the helical flight being continuous at least in that portion of thescrew in which the subjecting means is positioned.

32. The screw for advancing and working thermoplastic materials as setforth in claim 31, wherein:

the core is formed with at least a metering section,

and

the subjecting means is disposed in at least one plane positioned alongthe metering section.

33. An extruder screw for advancing and working thermoplastic materials,which comprises:

a core having an axis of rotation;

a helical flight extending outwardly from the core to a surface ofrevolution concentric with the axis of rotation of the core, the flightdefining a channel measured in a transverse direction between adjacentturns of the flight and extending in a longitudinal direction in ahelical path lengthwise of the screw;

the screw being formed with at least a feed section, a compressionsection, a compression relief section and a metering section, and

at least one plurality of pins extending radially outwardly from thecore towards the surface of revolution, all of the pins in any one turnof the flight being arranged substantially in a plane, the plane beingperpendicular to the axis of rotation of the core,

the helical flight being continuous in at least that section of thescrew containing the pins.

34. The extruder screw of claim 33, wherein the pins are located in themetering section of the screw.

35. The extruder screw of claim 34, wherein the plane in which the pinsare disposed is located one-half turn downstream of the compressionrelief section.

36. The extruder screw of claim 34, wherein the pins are arranged infour planes spaced evenly along the metering section of the screw, thefirst one of the planes being one-half turn downstream of thecompression relief section and the downstream one of the planes being atthe downstream end of the screw.

37. The extruder screw of claim 34, wherein the height of the pins isless than that of the flight.

38. The extruder screw of claim 34, wherein the height of the pins isthe same as that of the flight.

39. The screw of claim 34, wherein the upstream one of the planes ispositioned approximately threesixteenths inch downstream of thecompression relief section.

40. The screw of claim 34, wherein the pins are three-sixteenths inch indiameter and the axes of the pins are spaced at least one-quarter inchapart along an axis circumferentially of the core.

41. The screw of claim 34, wherein the ratio of the area of the rootsurface between projections to the area of the outwardly exposedsurfaces of the pins in any one portion of the core is between 0 and 1.

1. A method of advancing and working thermoplastic materials, whichincludes the steps of: revolving at least one channel about an axis ofrevolution to advance at least one thermoplastic material through thechannel along a predetermined path; and subjecting the material to atleast one plurality of forces exerted by force-producing componentsextending into the path and along axes which intersect the channel: allof the force-producing components in any one portion of the channelhaving at least some portion of the axis of each of the components inthe portion lying in a plane which is perpendicular to the axis ofrevolution; any portion of the channel extending between the walls ofthe channel and a predetermined distance along the axis of revolution;the walls of the channel being formed by continuous surfacesintersecting with the plane so that the walls of the channel areuninterrupted at the intersection with the plane.
 2. The method of claim1, wherein the channel is formed by a helical flight generated about theaxis of revolution.
 3. The method of claim 1, wherein the axes of allthe force-producing elements in any one portion of the channel liesubstantially in the plane.
 4. A method of advancing and workingthermoplastic materials, which includes the steps of: revolving at leastone channel about an axis of revolution to advance at least onethermoplastic material through the channel along a predetermined path;the walls of the channel being formed by turns of a flight formed aboutand along the axis of revolution; and subjecting the material to atleast one plurality of forces exerted by force-producing componentsextending into the path; all of the force-producing components in thechannel in any one turn of the flight having at least some portion ofeach of the components in the turn lying in a plane which isperpendicular to the axis of revolution; the walls of the channel beingformed by continuous surfaces, intersecting the plane so that thechannel is uninterrupted at the intersection with the plane.
 5. A methodof advancing and working thermoplastic materials, which includes thesteps of: rotating an extruder screw having at least one helical flightformed thereon about an axis of rotation to advance at least onethermoplastic material through a channel having walls formed by theflight; and subjecting the material to at least one plurality of forcesexerted by force-producing components extending into the channel andalong axes which intersect the channel; all the force-producingcomponents in the channel in any one turn of the flight having at leastsome portion of the axis of each of the components in the turn lying ina plane which is perpendicular to the axis rotation; the at least oneflight intersecting with the plane and being continuous therethrough. 6.The method of claim 5, wherein at least some portion of each one of allof the force-producing components in any one turn of the flight lies inthe plane.
 7. The method of claim 6, wherein all of the force-producingcomponents in any one turn of the flight lie substantially in the plane.8. A method of advancing and working thermoplastic materials, whichcomprises the steps of: advancing at least one thermoplastic materialthrough a helical channel extending along and about an axis ofrevolution; compressing the material; relieving the pressure in thematerial; and Homogenizing the material by subjecting the material to atleast one plurality of forces subsequent to relieving the pressure inthe material, the forces being exerted by force-producing components,all the force-producing components in the channel in any one turnthereof lying substantially in a plane which is perpendicular to theaxis of revolution and directed radially outward from the axis ofrevolution; the helical channel having uninterrupted side boundaries atleast along that portion of the predetermined path at which theforce-producing components are positioned.
 9. A method of advancing andworking thermoplastic materials, which comprises the steps of: moving acore having at least one helical flight formed therealong rotatablyabout an axis of rotation to advance a thermoplastic material along apredetermined path; compressing the material; relieving the pressure inthe material; and subjecting the material to at least one plurality offorces subsequent to relieving the pressure in the material, the forcesbeing exerted by force-producing components; all of the force-producingcomponents along the core in any one turn of the flight having at leastsome portion thereof lying in a plane which is perpendicular to the axisof rotation; the flight intersecting with and being continuous throughthe plane.
 10. The method of claim 9, wherein each one of theforce-producing components in any one turn of the flight liessubstantially in the plane.
 11. The method of claim 10, whereinforce-producing components are directed radially outward from the axisof rotation.
 12. A method of advancing and working thermoplasticmaterials, which comprises the steps of: introducing at least onethermoplastic material into engagement with a first zone of a screwmounted rotatably in a housing, the screw having a helical flight formedthereon; moving the screw rotatably about an axis of rotation to feedthe thermoplastic materials longitudinally along the screw through achannel formed on the screw to a second zone of the screw; compressingthe thermoplastic material in the second zone of the screw while thematerial is advanced simultaneously through the second zone to a thirdzone; relieving the pressure in the thermoplastic material in a thirdzone of the screw while the material is advanced through the third zoneto a fourth zone; and advancing the thermoplastic material through afourth metering zone of the screw while simultaneously homogenizing thematerial by subjecting the material to at least one group of a pluralityof forces exerted by force-producing components spaced about the surfaceof the screw and extending into the channel, all of the force-producingcomponents creating the forces being in a metering zone of the screw andall of the force-producing components along the metering zone of thescrew in any one turn of the flight lying in a plane perpendicular ofthe axis of rotation of the screw, being directed radially outward fromthe axis of rotation, and being non-intersecting with the flight.
 13. Anapparatus for advancing and working thermoplastic materials, whichcomprises: at least one channel having a base and side walls, thechannel being generated about an axis of revolution; means for revolvingthe at least one channel about the axis of revolution to advance atleast one thermoplastic material through the channel along apredetermined path; and at least one plurality of force-producingcomponents extending into the path and along axes which intersect thebase of the channel for subjecting the material to at least oneplurality of forces; all of the force-producing components in thechannel in any one turn thereof having at least some portion of the axisof each of the components in the section lying in a plane which isperpendicular to the axis of revolution; the walls of the channel beingformed by surfaces intersecting with the plane so that the channel wallSare uninterrupted at the intersection with and are continuous throughthe plane.
 14. An apparatus for advancing and working thermoplasticmaterials, which comprises: at least one channel having a base and sidewalls, the channel being generated about an axis of revolution; meansfor revolving the at least one channel about the axis of revolution toadvance at least one thermoplastic material through the channel along apredetermined path; and at least one plurality of force-producingcomponents extending into the path for subjecting the material to atleast one plurality of forces; all of the force-producing components inthe channel in any one turn thereof having at least some portion of eachof the components in the turn lying in a plane which is perpendicular tothe axis of revolution; the walls of the channel being formed bysurfaces intersecting with the plane so that the channel walls areuninterrupted at the intersection with and are continuous through theplane.
 15. The apparatus of claim 14, wherein the channel is formed by ahelical flight generated about the axis of revolution.
 16. Apparatus foradvancing and working thermoplastic materials, which comprises: achannel generated helically about an axis for advancing at least onethermoplastic material along a predetermined path; means for revolvingthe channel about the axis; and at least one plurality offorce-producing components extending into the path along axes whichintersect the channel and positioned along the axis of revolution forsubjecting the material to a plurality of forces, all of theforce-producing components in the channel in any one turn thereof havingat least a portion of the axis thereof lying in a plane which isperpendicular to the axis of revolution; the walls of the channel beingformed by surfaces, which surfaces intersect with the plane and whichsurfaces are continuous through the plane.
 17. Apparatus for advancingand working thermoplastic materials, which comprises; a housing having alongitudinally extending bore formed therein and having a longitudinalaxis; means disposed concentrically within the bore and having a flightformed helically thereon and extending substantially from one endthereof to the other for advancing a thermoplastic material from the oneend to the other end thereof; means for rotating the advancing meansabout the longitudinal axis; and a plurality of means connected to theadvancing means for homogenizing the thermoplastic material, all of thehomogenizing means in any one turn of the flight being disposedsubstantially in one plane perpendicular to the longitudinal axis; thehelical flight being continuous in at least the portion of the advancingmeans which contains the homogenizing means.
 18. Apparatus for advancingand working thermoplastic materials, which comprises: means including atleast one channel for advancing at least one thermoplastic materialalong a predetermined path through the channel extending along thepredetermined path; and means for revolving the channel around an axisof revolution; and a plurality of means in the advancing means anddirected radially outward from the axis of revolution for homogenizingthe material; all the means in any one turn of the channel lyingsubstantially in a plane which is perpendicular to the axis ofrevolution; the walls of the channel being formed by surfaces, whichsurfaces intersect with the plane and are continuous therethrough so asto have uninterrupted boundaries at least along that portion of thepredetermined path containing the homogenizing means.
 19. Apparatus foradvancing and working thermoplastic materials, which comprises: ahousing having a longitudinally extending cylindrical bore formedtherein, an extrusion screw fitting closely within the bore and having achannel extending substantially from one end to the other end thereofgenerated helically about an axis of rotatioN of the screw, one end ofthe screw being a receiving end and the other end being a delivery end,for advancing a thermoplastic material from the receiving end of thescrew to the delivery end thereof and for homogenizing the material; thescrew being formed successively from the receiving end to the deliveryend with a feed section, a compression section, a compression reliefsection, and a metering section, and a plurality of means in the channelfor subjecting the thermoplastic materials to a plurality of forces; allthe means in any one turn of the channel having at least an integralportion thereof disposed in one plane which is perpendicular to the axisof rotation of the screw; the walls of the channel being formed bysurfaces intersecting with the plane so that the surfaces areuninterrupted and continuous through the plane.
 20. The apparatus ofclaim 19, wherein the subjecting means is disposed within the meteringsection of the screw.
 21. The apparatus of claim 19, wherein thesubjecting means includes at least one group of a plurality offorce-producing components with all of the force-producing components inany one turn of the channel having at least a portion of each of theforce-producing components in that turn lying in the plane.
 22. Theapparatus of claim 21, wherein all the force-producing components arepositioned along the metering section of the screw, all of theforce-producing components in any one turn of the metering section ofthe screw lying substantially in the plane.
 23. The apparatus of claim22, wherein the upstream one of the at least one group of components isspaced less than one turn downstream of the compression relief sectionof the screw.
 24. The apparatus of claim 23, wherein a second group offorce-producing components are positioned at the downstream end of thescrew.
 25. The apparatus of claim 24, wherein at least four groups ofthe force-producing components are spaced along the metering section ofthe screw, the middle two groups of components being equally spacedalong the metering section between the upstream-most group and thedownstream-most group.
 26. The apparatus of claim 19, wherein thesubjecting means includes one group of a plurality of pins arrangedabout the circumference of the screw, all of the pins in the at leastone group lying substantially in the plane all of the pins being withinthe metering section of the screw.
 27. The apparatus of claim 26,wherein the pins are directed radially perpendicularly of the axis ofrotation of the screw.
 28. The apparatus of claim 27, wherein theupstream one of the planes is spaced one-half the pitch of the screwdownstream of the downstream end of the compression relief section ofthe screw.
 29. A screw for advancing and working thermoplasticmaterials, which comprises: a core having an axis of rotation foradvancing a thermoplastic material; at least one flight connected to andextending outwardly from the core to a surface of revolution concentricwith the axis of rotation of the core, the flight being generatedhelically about the axis of rotation; and at least one plurality offorce-producing components connected to the core for subjecting thematerial to a plurality of forces, the force-producing componentsextending beyond the core along axes which intersect the core and spacedfrom the surface of revolution, all of the force-producing componentsalong the core in any one turn of the flight having at least someportion of the axis of each of the components in the turn of the flightlying in a plane which plane is perpendicular to the axis of rotation;the flight intersecting with and being continuous through the plane. 30.A screw for advancing and working thermoplastic materials, whichcomprises: a core having an axis of rotation for advancing athermoplastic material; at least one flight connected to and extendingoutwardly from the core to a surface of revolution concentric with theaxis of rOtation of the core, the flight being generated helically aboutthe axis of rotation; and at least one plurality of force-producingcomponents connected to the core for subjecting the material to aplurality of forces, the force-producing components extending beyond thecore and spaced from the surface of revolution, all of theforce-producing components along the core in any one turn of the flighthaving at least some portion of each of the components in the turn ofthe flight lying in a plane which plane is perpendicular to the axis ofrotation; the flight intersecting with and being continuous through theplane.
 31. A screw for advancing and working thermoplastic materials,which comprises: a core having an axis of rotation; at least one helicalflight extending outwardly from the core to a surface of revolutionconcentric with the axis of rotation of the core, the at least oneflight defining a channel measured in a transverse direction betweenadjacent turns of the flight, and extending in a helical path lengthwiseof the core; and a plurality of means for subjecting a thermoplasticmaterial to a plurality of forces to homogenize the material; all themeans in any one turn of the flight disposed substantially in one planewhich is perpendicular to the axis of rotation of the core; the helicalflight being continuous at least in that portion of the screw in whichthe subjecting means is positioned.
 32. The screw for advancing andworking thermoplastic materials as set forth in claim 31, wherein: thecore is formed with at least a metering section, and the subjectingmeans is disposed in at least one plane positioned along the meteringsection.
 33. An extruder screw for advancing and working thermoplasticmaterials, which comprises: a core having an axis of rotation; a helicalflight extending outwardly from the core to a surface of revolutionconcentric with the axis of rotation of the core, the flight defining achannel measured in a transverse direction between adjacent turns of theflight and extending in a longitudinal direction in a helical pathlengthwise of the screw; the screw being formed with at least a feedsection, a compression section, a compression relief section and ametering section, and at least one plurality of pins extending radiallyoutwardly from the core towards the surface of revolution, all of thepins in any one turn of the flight being arranged substantially in aplane, the plane being perpendicular to the axis of rotation of thecore, the helical flight being continuous in at least that section ofthe screw containing the pins.
 34. The extruder screw of claim 33,wherein the pins are located in the metering section of the screw. 35.The extruder screw of claim 34, wherein the plane in which the pins aredisposed is located one-half turn downstream of the compression reliefsection.
 36. The extruder screw of claim 34, wherein the pins arearranged in four planes spaced evenly along the metering section of thescrew, the first one of the planes being one-half turn downstream of thecompression relief section and the downstream one of the planes being atthe downstream end of the screw.
 37. The extruder screw of claim 34,wherein the height of the pins is less than that of the flight.
 38. Theextruder screw of claim 34, wherein the height of the pins is the sameas that of the flight.
 39. The screw of claim 34, wherein the upstreamone of the planes is positioned approximately three-sixteenths inchdownstream of the compression relief section.
 40. The screw of claim 34,wherein the pins are three-sixteenths inch in diameter and the axes ofthe pins are spaced at least one-quarter inch apart along an axiscircumferentially of the core.
 41. The screw of claim 34, wherein theratio of the area of the root surface between projections to the area ofthe outwardly exposed surfaces of the pins in any one portion of thecore is between 0 and 1.